Fuel-injection pump for internal-combustion engines

ABSTRACT

A fuel-injection pump, especially a direct fuel injection in spark-ignition internal-combustion engines, with at least one pump for generating a fuel flow under pressure and with a rotary slide valve moved synchronously with the drive shaft of the internal-combustion engine and intended for assigning the fuel flow to at least one injection port of the internal-combustion engine and/or for branching off the fuel flow under pump pressure into a return line, the rotary slide valve is mounted so as to be displaceable to a limited extent in the direction of its axis of rotation and/or so as to be rotatable to a limited extent in relation to the rotary drive of the rotary slide valve. Preferably, at the same time, the rotary position or displacement position of the rotary slide valve can be determined in dependence on an operating parameter of the internal-combustion engine, with the result that the axial displacement of the rotary slide valve counteracts a seizure of the rotary slide valve in its guide and determination in dependence on operating parameters affords the possibility of adjusting the injection time over a larger angular sector than would be possible in view of the geometrical limits placed on the design of the rotary slide valve.

The invention relates to a fuel-injection pump.

A fuel-injection pump of this type is to be taken, for example, from theolder German Application P 3,804,025, now U.S. Pat. No. 4,879,984. Inthis older version of a fuel-injection pump, the fuel flow wasdistributed by a plurality of pumps to the injection ports of injectionvalves by means of a rotary slide valve which was synchronously drivenin rotational movement at a predetermined transmission ratio relative tothe engine shaft. The injection quantity and injection time werecontrolled by opening or closing an overflow channel to a relief volumeby means of a solenoid valve. When it is necessary to distribute thefuel flow to a plurality of cylinders of an internal-combustion engine,with the increasing number of cylinders of the internal-combustionengine there is a reduction of the particular angular sector of therotary slide valve which is available for geometrical reasons and overwhich the injection quantity and the injection time for an individualcylinder can be influenced by means of the solenoid valve. Afteroperating for a relatively long period of time, a rotary slide valvedriven simply in rotational movement tends to exhibit signs of wearwhich in turn cause the rotary slide to seize in its guide.

The fuel-injection pump according to the invention affords thepossibility, by means of an axial displacement of the rotary slidevalve, of counteracting a seizure of the rotary slide valve in itsguide. At the same time, an axial displacement of the rotary slidevalve, with an appropriate design of the circumferentially extendingrecesses for distributing the fuel flow to individual cylinders, and/ora relative rotation of the rotary slide valve in relation to the rotarydrive allows the possibility of adjusting the injection time over alarger angular sector than would be possible otherwise in view of thegeometrical limits placed on the configuration of the circumferentiallymeasured length of the grooves of the rotary slide valve which serve fordistribution. Particularly in internal-combustion engines with more thanfour cylinders, without an additional possibility of influencing theshift of the injection time, the geometrical limits of the rotary slidevalve itself are already clearly detectable.

To shift the effective angular sector for distributing the fuel flow toan injection port of a particular cylinder of the internal-combustionengine, advantageously the design is such that the rotary slide valvecan be fixed in its rotary position or displacement position independence on an operating parameter of the internal-combustion engine.Considered as an operating parameter of the internal-combustion enginehere is primarily the speed of the internal-combustion engine or else acontrol variable related to the speed of the internal-combustion engine,such as, for example, the fuel pressure of a fuel pump driven insynchronism with the engine shaft, an oil pressure or the like. Thecorresponding control variable can also be derived from a centrifugalgovernor.

To influence the particular desired displacement position of the rotaryslide valve dependent on an operating parameter in the direction of itsaxis of rotation, the rotary slide valve can advantageously bedisplaceable in the direction of this axis of rotation against a stopadjustable in dependence on an operating parameter. The measure ofproviding a separate stop of this type makes it possible in a simple wayto utilise a pressure dependent on an operating parameter for adjustingthe stop, advantageously the design being such that the adjustable stopis formed by a stop piston which can be subjected hydraulically tospeed-dependent pressure. Instead of a separate stop piston of thistype, the rotary slide valve itself can also be designed in a simple wayas a piston, in which case subjecting such a rotary slide valve designedas a piston to a pressure medium on the piston end face can be utiliseddirectly for displacing the rotary slide valve, and advantageously theworking space of this piston can be subjected to a pressure mediumcounter to the force of a spring acting on the rotary slide valve. Apressure suitable for the purpose of displacing the rotary slide valvecan be derived directly from the high-pressure side of the pump, and ifthe rotary slide valve designed as a piston is subjected to a pumppressure of this kind the design is preferably such that the workingspace of the rotary slide valve designed as a piston is connected to thereturn line via a throttle and, if appropriate, a relief valve. The pumppressure is at the same time reduced via the throttle, and, in view ofthe dynamic flow behaviour of the fuel, a displacement pressurecorresponding to an operating parameter of the internal-combustionengine occurs on that side of the rotary slide valve which is designedas a piston. In all instances where the rotary slide valve is merelydisplaced in the axial direction of its axis of rotation and wherespecial modifications have not at the same time been made to thecircumferentially extending grooves for distributing the fuel flow tothe cylinders, the axial displacement initially only affords theadvantage of counteracting a seizure of the rotary slide valve. But if,in addition, the design of the circumferentially extending grooves ofthe rotary slide valve which serve for distribution is changed or arotation of the rotary slide valve relative to its drive is executed,the angular sector over which it is possible for the injection operationto be influenced by the solenoid valve can be adjusted. Advantageously,here, the design can be such that the rotary slide valve is coupled tothe rotary drive via oblique teeth or grooves. During an axialdisplacement of the rotary slide valve, such a coupling of the rotaryslide valve to the rotary drive via oblique teeth or grooves leads atthe same time, because of the oblique teeth or grooves, to a relativerotation of the rotary slide valve in relation to the rotary drive. Inan especially simple way, here, the design can be such that the rotaryslide valve engages via at least one bolt oriented essentially radiallyrelative to the axis of rotation into an oblique groove on the innercircumference of a hollow driving wheel connected to the rotary drive,thereby ensuring an especially compact design.

The synchronous rotary drive of the rotary slide valve can be deriveddirectly from the engine shaft in a simple way. To obtain a uniformpressure level even when there is only a small number of piston pumps,the pump camshaft can be driven at the correspondingly lowest possiblespeed, but a speed higher than that of the drive shaft of the rotaryslide valve, for which purpose the design is advantageously such thatthe hollow driving wheel of the rotary slide valve is designed as agear-wheel meshing with a gearwheel of a pump camshaft, and such thatthe gearwheel of the pump camshaft has a smaller diameter than thehollow driving wheel of the rotary slide valve.

When a shift of the angular sector effective for controlling theinjection operation is to be achieved by means of a simple axialdisplacement of the rotary slide valve without a relative rotation ofthe rotary slide valve in relation to its rotary drive, this can beachieved in a simple way, if the rotary slide valve has on itscircumference control grooves extending obliquely relatively to theaxis. If such control grooves extending obliquely relative to the axisare provided, the width of these control grooves can correspondessentially to the diameter of the bores opening on to the controlgrooves. But if an axial displacement of the rotary slide valve togetherwith a relative rotation of the rotary slide valve in relation to itsdrive is to be permissible in order to adjust the effective angularsector, advantageously the design is such that the circumferentialgrooves of the rotary slide valve have an axially measured width whichis at least equal to the maximum axial displacement travel of the rotaryslide valve occurring during the rotation of the rotary slide valve inrelation to its rotary drive. Likewise, during the axial displacement ofthe rotary slide valve, it is necessary to ensure that fuel is fed underpressure in each axial displacement position, for which purpose thedesign is advantageously such that a circumferential groove of therotary slide valve connected to the pump delivery connection has a widthin the axial direction corresponding to the maximum axial displacementtravel of the rotary slide valve.

To achieve a fluid pressure suitable for displacing the rotary slidevalve in the axial direction, in a simple way the design can be suchthat the injection time and the injection period or quantity can befixed by means of a solenoid valve opening into the return and connectedto a delivery line of the pump or pumps, and such that the solenoidvalve is connected to the return, with the working space of the rotaryslide valve designed as a piston or the working space of a regulatingpiston and a throttle being interposed, thereby at the same timeensuring especially compact constructional dimensions.

To ensure that a reproducible injection quantity is obtainedirrespective of the number Z of engine cylinders, care is taken toensure, by the choice of the transmission ratio of pump speed to enginespeed, that the pump feed rate during injection is always the same fromcylinder to cylinder. Where a 3-cylinder eccentric pump is concerned,the ratio is preferably selected according to the formula (Z.120°)/720°.

The invention is explained in more detail below by means of exemplaryembodiments illustrated diagrammatically in the drawing. In this, FIG. 1shows a partial section through a first embodiment of a fuel-injectionpump according to the invention in the region of the rotary slide valve;FIG. 2 shows a modified embodiment of a fuel-injection pump according tothe invention in a representation similar to that of FIG. 1; and FIG. 3shows a further modified embodiment, in which a seizure of the rotaryslide valve is largely to be prevented by means of an axial movement ofthe latter.

In FIG. 1, 1 denotes a pump casing of a distributor fuel-injection pump,in which a rotary slide valve 2 acting as a distributor is arrangedrotatably and axially displaceably in a cylindrical bore 3. The rotaryslide valve 2 is driven via a hollow gearwheel 4 which meshes with agearwheel 5 of a pump camshaft not shown in any more detail. At the sametime, the gearwheel 5 of the pump camshaft has a smaller diameter thanthe driving wheel 4 of the rotary slide valve 2, and by the relativesizes of the gearwheels 4 and 5 a desired transmission ratio can be setbetween the rotational speed of the pump camshaft, not shown in any moredetail, which feeds fuel under pressure to the rotary slide valve via afeed line 6 by means of a plurality of pump pistons, and the rotationalspeed of the rotary slide valve 2, the rotary slide valve 2 being drivenin synchronism with the drive shaft of the internal-combustion engineand always at half the speed of the drive shaft. Via the feed line,designated by 6, which constitutes the collecting line for the fuelunder pressure coming from the individual pump elements, the fuel underpressure enters an annular space 7 which is formed by a circumferentialrecess or groove extending in the axial direction of the rotary slidevalve 2. Furthermore, a line 9 leading to a solenoid valve 8 opens outin the region of the circumferential groove 7 of the rotary slide valve2, the solenoid valve 8 controlling both the start of injection and theinjection quantity or injection period. The fuel under pressure, cut offvia the solenoid valve in its opened position, passes via a bore 10 intoa working space 11 limited by the rotary slide valve 2 and belonging tothe rotary slide valve designed at the same time as a stop piston, inorder to achieve a larger possible injection range by means of an axialdisplacement of the rotary slide valve 2 and/or a relative rotation ofthe latter in relation to its rotary drive, as will also be explained inmore detail later. At the same time, the pressure in the working space11 is adjusted via a pressure-holding valve 12, and the fuel issuingfrom the working space 11 flows into a return line, indicateddiagrammatically at 13, to the tank.

For an injection, after the solenoid valve 8 has closed the fuel underpressure passes out of the annular space or circumferential groove 7 ofthe rotary slide valve into a bore 15 extending obliquely relative tothe axis 14 of the rotary slide valve, to a recess or groove 16 which isarranged on the circumference of the rotary slide valve and which, in anappropriate rotary position of the rotary slide valve, delivers fuelunder pressure via a feed line 17 to an injection valve 18 indicateddiagrammatically. For pressure compensation, a pressure-compensatingbore 19 located in the rotary slide valve opens into the recess 16 at anangle corresponding to the angle of the bore 15.

According to the number of cylinders of the internal-combustion engine,a corresponding number of feed bores to the individual injection valvesof the engine cylinders are provided in a uniform distribution, in asimilar way to the bore 17, and for separating the respective injectionoperations in the individual cylinders there is only a restrictedangular sector available during the rotational movement of the rotaryslide valve 2 taking place in synchronism with the engine shaft. So thatthe angular sector useful for an injection can be varied within widerlimits than those governed by the geometrical conditions, the rotaryslide valve 2 is displaced and/or rotated in relation to the drivinggearwheel 4. For this purpose, on the rotary slide valve 2 there are twobolts 20 which extend essentially radially relative to the axis 14 ofthe rotary slide and which engage into diagrammatically indicatedgrooves 21 extending obliquely relative to the axis 14 of the rotaryslide and located on the inner circumference of the driving gearwheel 4.During an axial displacement of the rotary slide valve 2, a rotation ofthe rotary slide valve 2 relative to the driving wheel 4 takes placesvia the radial bolts 20 engaging into the oblique grooves 21, andsubsequently the recess 16 comes at another moment in time, that is tosay in another angular sector of the engine drive shaft, into a positionaligned with a bore 17 to an injection valve, so that the start ofinjection can thereby be adjusted within wide limits. At the same time,via the pressure prevailing in the working space 11, the rotary sidevalve is held bearing against a control piston 22 which is loaded by aspring 23. The control piston is loaded via a diagrammatically indicatedfeed line 24 in dependence on an operating parameter, such as, forexample, the engine-oil pressure or the petrol inflow pressure. Asmentioned above, the resulting axial movement of the control piston andtherefore of the rotary slide valve is converted, via the radial boltsrunning in the oblique groove 21, into a rotational movement of therotary slide valve 2 in relation to the pump drive shaft and thereforeto the engine drive shaft. To allow for the axial displacement of therotary slide valve 2, both the recess 7 interacting with the inflow 6and the recess 16 interacting respectively with an injection valve viathe bore 17 have a width in the direction of the axis of the rotaryslide valve which is at least equal to the maximum axial displacementtravel of the rotary slide valve 2.

Instead of rotating the rotary slide valve 2 relative to the drivingwheel 4 via radial bolts or pins engaging into oblique grooves, ahelical toothing can also be provided on the rotary slide valve 2 and onthe inner circumference of the driving wheel 4, in order thereby toconvert an axial movement of the rotary slide valve 2 into a relativerotation in relation to the driving wheel 4.

In FIG. 1, furthermore, 25 denotes a leakage bore which interacts with acircumferential groove 26 on the rotary slide valve 2.

In the embodiment according to FIG. 2, the reference symbols of FIG. 1have been preserved for identical components. Here, once again, an axialmovement of the rotary slide valve 2 is converted into a rotationalmovement of the latter relative to the driving wheel 4 in order toadjust the angular sector useful for an injection. At the same time, therotary slide valve is subjected to stress in the axial direction via apiston 28 loaded by a spring 27, and the axial displacement of therotary slide valve 2 designed as a piston, taking place in the workingspace 11, is utilised for adjusting the axial position and therefore therotary position relative to the driving wheel. Thus, the fuel flow cutoff by the solenoid valve 8 passes out of the working space 11 via athrottle 29 into the return 13 to the tank. With an increasing speed,the fuel quantity entering the working space 11 increases, and there istherefore established in the space 11 a higher mean pressure level, bymeans of which the rotary slide valve 2 is displaced towards thespring-loaded piston 28. Furthermore, a relief valve 31 is inserted in abypass line 30 relative to the throttle 29, so that after the regulatingdistance has been covered, that is to say after the piston 28 comes tobear against the stop 32, the relief valve opens into the return line13. At the same time, the throttle 29 and the prestressing force of thespring 27 are coordinated in such a way that an axial movement of therotary slide valve takes place only beyond a predetermined speed.Furthermore, strong pressure pulsations which possibly occur in theworking space 11 and which would lead to indeterminate movements of therotary slide valve 2 can be damped or smoothed as a result of anappropriate design of the spring characteristic.

Instead of converting an axial displacement of the rotary slide valveinto a relative rotation in relation to the driving wheel 4 for varyingthe angular sector useful for an injection, it would also be possible todisplace the rotary slide valve 2 in the axial direction only. Thus,instead of the circumferential groove or recess 16 which extends over awidth corresponding to the maximum axial displacement travel and whichinteracts with the individual inflow bores 17 to the injection valves18, this circumferential groove is arranged obliquely relative to theaxis 14 of the rotary slide valve 2, so that in the event of an axialdisplacement of the rotary slide valve 2 in different rotary positionsthe feed bores 17 are crossed, and in this case, of course, thecircumferential recess 16 would have to extend over an angular sectorlarger than that of the embodiment illustrated in FIGS. 1 and 2.

FIG. 3 shows a modified embodiment of the rotary slide valve 2 which isonce again connected to the pump drive shaft or the engine shaft via adriving wheel 4 in a way not shown in any more detail. By way of theinflow bore 6, fuel passes into a axial channel 34 of the rotary slidevalve 2 via recesses 33 provided on the circumference of the rotaryslide valve, and in corresponding angular positions fuel under pressureenters feed lines 36 to injection valves via recesses 35 arranged in afurther plane. Via the axial channel 34, a further circumferentialgroove 37 is connected to a relief bore 38, in which is inserted asolenoid valve 39 similar to the solenoid valve 8. The fuel flow cut offvia the solenoid valve 39 once more passes via a line 40 into a workingspace 41 which is connected to a return 42. Since a pressure wave istriggered in the return whenever the fuel flow is cut off, the rotaryslide valve 2 is thereby subjected to stress in the axial direction andmoved in the axial direction counter to the force of a spring 43. Since,in contrast to the design according to FIGS. 1 and 2, neither apressure-holding valve nor a throttle and a relief valve are inserted inthe return 42, after the pressure wave occurs, the pressure in theworking space 41 drops quickly again and the rotary slide valve 2 isonce more moved back into its normal position by the force of the spring43. An oscillating axial movement of the rotary slide valve 2 is therebysuperposed on the rotational movement, and this oscillating movement canprevent a seizure of the rotary side valve 2. This ensures morefavourable lubrication conditions which are of considerable importanceespecially in a petrol-driven engine. In contrast to the embodimentsaccording to FIGS. 1 and 2, therefore, in this embodiment the rotaryslide valve 2 is not fixed in the axial displacement position and/or therelative rotary position in relation to the driving wheel 4, which areselected in dependence on operating parameters, so that no adjustment ofthe angular sector useful for an injection is carried out.

We claim:
 1. A fuel injection pump for direct fuel injection in internalcombustion engines having a drive shaft and with externally suppliedignition, at least one pump for generating a fuel stream with pressurebrought to an injection pressure, a rotary slide valve which is movedsynchronously with the drive shaft of the engine, said rotary slidevalve has a distributor opening on a jacket face that upon a rotation ofthe rotary slide, said distributor opening comes to coincide with one ofa plurality of pressure lines distributed over a circumference of therotary slide and which lead away from a bore that receives the rotaryslide, each of said pressure lines leads to one injection location ofthe engine, and the distributor opening communicates continuously withthe at least one pump and with a relief line in which an electricallycontrolled valve is disposed and by a closing state said electricallycontrolled valve controls a high-pressure feeding of fuel from thedistributor opening to the injection locations, the injection line,downstream of the electrically controlled valve, discharges into a workchamber enclosed by a face end of the rotary slide in the bore, saidwork chamber is relieved in throttled fashion and the rotary slide isdisplaceable axially counter to a restoring force.
 2. A fuel injectionpump as defined by claim 1 in which a pressure limiting valve forthrottling a relief of the work chamber is disposed in a return lineleading away from the work chamber toward the relief side.
 3. A fuelinjection pump as defined by claim 2 in which a fixed throttle isdisposed parallel to the pressure limiting valve and means are providedby which upon displacement of the rotary slide, the rotary position ofthe distributor opening relative to the rotary position of the driveshaft is variable.
 4. A fuel-injection pump, especially for direct fuelinjection in spark-ignition internal combustion engines, comprising atleast one pump for generating a fuel flow under pressure and with arotary slide valve moved synchronously with a drive shaft of theinternal combustion engine and intended for assigning the fuel flow toat least one injection port of the internal combustion engine and forbranching off the fuel flow under pressure into a return line, in whichthe rotary slide valve (2) is provided with at least one bolt (20) whichis oriented essentially radially relative to the axis of rotation of therotary slide valve (2) which engages an oblique groove (21) on an innercircumference of a hollow driving wheel (4) connected to the rotarydrive so that the rotary slide valve is displaceable to a limited extentin a direction of its axis of rotation (14) and rotatable to a limitedextent in relation to the rotary drive of the rotary slide valve (2). 5.A fuel-injection pump according to claim 4 in which the rotary positionor displacement position of the rotary slide valve (2) is determined independence on an operating parameter of the internal combustion engine.6. A fuel-injection pump according to claim 4 in which the rotary slidevalve (2) is displaceable in a direction of its axis of rotation (14)against a stop adjustable in dependence on an operating parameter.
 7. Afuel-injection pump according to claim 1, which the rotary slide valve(2) is displaceable in a direction of its axis of rotation (14) againsta stop adjustable in dependence on an operating parameter.
 8. Afuel-injection pump according to claim 1, in which the adjustable stopis formed by a stop piston (22) which can be subjected hydraulically toa speed-dependent pressure.
 9. A fuel-injection pump according to claim1, in which the rotary slide valve (2) is coupled to the rotary drivevia oblique teeth or grooves.
 10. A fuel-injection pump according toclaim 4, in which the hollow driving wheel (14) of the rotary slidevalve (2) is designed as a gearwheel meshing with a gearwheel (5) of apump camshaft, and in that the gearwheel (5) of the pump camshaft has asmaller diameter than the hollow driving wheel (4) of the rotary slidevalve (2).
 11. A fuel-injection pump according to claim 1, in which therotary slide valve (2) has on its circumference control groovesextending obliquely relative to the axis.
 12. A fuel-injection pumpaccording to claim 1, in which the circumferential grooves (16) of therotary slide valve (2) have an axially measured width which is at leastequal to the maximum axial displacement travel of the rotary slide valve(2) occurring during the rotation of the rotary slide valve (2) inrelation to its rotary drive.
 13. A fuel-injection pump according toclaim 1, in which a circumferential groove (7) of the rotary slide valve(2) connected to the pump delivery connection (6) has a width in theaxial direction corresponding to the maximum axial displacement travelof the rotary slide valve (2).
 14. A fuel-injection pump according toclaim 1 which includes a three-cylinder eccentric pump in which atransmission ratio of pump speed to engine speed is selected accordingto the factor (Z.120°)/720°, Z representing the number of enginecylinders.
 15. A fuel-injection pump according to claim 7, in which theadjustable stop is formed by a stop piston (22) which can be subjectedhydraulically to a speed-dependent pressure.
 16. A fuel-injection pumpaccording to claim 7, in which the rotary slide valve (2) is designed asa piston, the working space (11, 41) which can be subjected to apressure medium counter to the force of a spring (27, 43) acting on therotary slide valve (2).
 17. A fuel-injection pump according to claim 7,in which the rotary slide valve (2) is coupled to the rotary drive viaoblique teeth or grooves.
 18. A fuel-injection pump according to claim7, in which the rotary slide valve (2) has on its circumference controlgrooves extending obliquely relative to the axis.
 19. A fuel-injectionpump according to claim 7, in which the circumferential grooves (16) ofthe rotary slide valve (2) have an axially measured width which is atleast equal to the maximum axial displacement travel of the rotary slidevalve (2) occurring during the rotation of the rotary slide valve (2) inrelation to its rotary drive.
 20. A fuel-injection pump according toclaim 7, in which a circumferential groove (7) of the rotary slide valve(2) connected to the pump delivery connection (6) has a width in theaxial direction corresponding to the maximum axial displacement travelof the rotary slide valve (2).
 21. A fuel-injection pump according toclaim 7, in which the injection time and the injection period orquantity can be fixed by means of a solenoid valve (8, 39) which opensinto the return line and which is connected to a delivery line (9, 28)of the pump or pumps, and in that the solenoid valve (8, 39) isconnected to the return line (13, 42), with the working space (11, 41)of the rotary slide valve (2) designed as a piston or the working spaceof a regulating piston and a throttle being interposed.
 22. Afuel-injection pump according to claim 7 which includes a three-cylindereccentric pump in which a transmission ratio of pump speed to enginespeed is selected according to the factor (Z.120°)/720°, Z representingthe number of engine cylinders.